Hydraulic switches having an electrical switch controlled by a buoyant sensor are known. As the buoyant sensor moves from a lower position to a higher position, an electrical switch is closed and a circuit is completed. Prior switches, however, appear to be designed for stand pipes or static tank situations wherein a liquid level rises or falls slowly.
Also, there are switch mechanisms for pumps wherein a float senses liquid within a reservoir or chamber and, consequently, rises or falls to close or open an electrical switch. For example, U.S. Pat. No. 3,316,845 discloses a bilge pump having an enclosure within which a cup chamber contains an electrical motor with a shaft to the pump impeller. Adjacent to the cup chamber is a second chamber within which a float sensor moves along a rod. The float moves between a pair of stops. When the float reaches the top stop, the rod is moved upwardly to close an electrical switch. When the float reaches the bottom stop, the rod is moved downwardly to open the electrical switch. Water enters the enclosure and passes through the lower portion of the second chamber before reaching the pump impeller. As the water level rises within the enclosure, the trapped air compresses and prevents water from passing over the lips of the cup so as to dampen and harm the motor. Thus, this bilge pump must be carefully designed to provide for a proper relationship between impeller speed, size and density of the float, and height of the float chamber relative to the size of the enclosure since such size affects the ultimate air pressure and the height of any rising water.
In a co-pending application assigned to the same assignee as the present application, now issued as U.S. Pat. No. 4,345,879, an hydraulic switch is disclosed which has a fluid line to a float reservoir from the exhaust side of the pump impeller. Although this latter hydraulic switch overcomes the need for close attention to certain design details important for the previously discussed patent, it requires a separate switch reservoir. Hence, the switch is not applicable to many applications.